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排序方式: 共有129条查询结果,搜索用时 34 毫秒
1.
为了评估北盘江鱼类增殖放流效果,2017~2018年期间采用体外荧光、剪鳍、"T"型标三种标志方法对目标鱼类进行标志放流,通过集中捕捞方式进行回捕调查,集中捕捞时间为2017年7月、2018年8月,捕捞水域为董菁-马马崖-光照-善泥坡库区。结果表明,白甲鱼回捕率较高,为0.82%,其他鱼类均在0.5%左右,其中主要为低龄鱼类,高龄鱼类较少;董菁打邦河及各库尾水域物种丰富度较高,善泥坡高家渡码头和马马崖库区试验库尾物种多样性指数相对较低。建议在以后的增殖放流活动中,加大每年的监测频次。 相似文献
2.
在上篇对于1927年魏森霍夫住宅博览会回顾与审视的基础上,此篇述及两次当代中国建筑展, 论述了展览内容、过程、机制等因素对于它所能具有的“厚度”的影响,以及就建筑展览的批判性内涵而言,作为一种特殊建筑类型的社会住宅的价值。最后并反思了建筑领域内展览行为的当代意义及建筑师在此类展览中通常采取的姿态。 相似文献
3.
Petra Lindemann-Matthies 《Landscape Research》2017,42(5):482-497
This study investigates with the help of a manipulative experiment how people with different nationalities perceive meadow-like arrays of different species richness (1, 8, 16, 32, 64 species). Participants (n = 187) were all residents of the canton of Zurich and originated from 43 different countries. Overall valuation of the meadow-like arrays increased with species richness. However, while participants from high-income countries (measured by GDP per capita) clearly liked species-rich meadows most and species-poor ones least, participants from low-income countries did not have such clear preferences. Preferences were not related to the length of time a participant had already spent in Switzerland (on average seven years), but to perceived familiarity with a meadow-like array. Sex and education did not influence valuations. Environmental expertise fostered participants’ dislike of species-poor arrays, as did age. 相似文献
4.
Giancarlo Marafioti Robert R. Bitmead Morten Hovd 《International Journal of Adaptive Control and Signal Processing》2014,28(6):536-552
Model predictive control (MPC) is a well‐known and widely used advanced control technique, which is model‐based and capable of handling both input and state/output constraints via receding horizon optimization methods. Fundamentally, MPC is a nondynamic or memoryless state feedback control. Because of its use of a model, MPC should be amenable to adaptive implementation and to on‐line tuning of the model. Such an approach requires guaranteeing signal properties, known as ‘persistent excitation’, to ensure uniform identifiability of the model, often expressed in terms of spectral content or ‘sufficient richness’ of a periodic input. We propose an approach to augment the input constraint set of MPC to provide this guarantee. This, in turn, requires equipping the controller with its own state to capture the control signal history. The feasibility of periodic signals for this condition is established. A computational example is presented illustrating the technique and its properties. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
5.
The impact of a large lowland temperate zone reservoir on chironomid and fish biodiversity was investigated in the same upstream (U) and downstream (D) sites on the same sampling occasions in spring and autumn of several post‐impoundment years. The true/Hill N1 diversity measure was used to construct diversity models of the impact, and partitioning of N1 to reveal the importance of ecological gradients. N1 is unique in being decomposable among multiple levels and easily comparable across ecosystems and animal groups. Chironomids were more diverse than fish in all community sets owing to their probably lower mobility, lower interspecific competition, opportunistic character and much shorter life spans than those of fish. Fish exerted consumption pressure on chironomids upstream by foraging mostly on benthic insects, but not downstream where they fed on microcrustaceans of reservoir origin or on epiphytic fauna (mainly Chironomidae). The reservoir impact on chironomids decreased their diversity in U and increased in D, while much the opposite was true in fish. In D in macroinvertebrates, the impact consisted in advancing over time intensification of seasonal development of submersed macrophytes, while in D in fish in a few species escaping from the reservoir after their populational explosions each year. Partitioning of diversity revealed that the spatial (upstream–downstream) gradient was the strongest factor of diversity change in chironomids as compared with season, and age of the impoundment. No gradient was dominant in fish. Comparisons of observed data with a null model testified to very strong intraspecific aggregation in both chironomids and fish. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
6.
张英伟 《北方工业大学学报》2007,19(2):70-74
叙述是散文创作必不可缺的,叙事者以什么样的叙述视角展开叙述,其叙述语言将会呈现出不同的审美效应。散文一般都是用第一、第二、第三人称完成一个文本的叙述过程,以第一、第二人称展开的叙事文本,其语言呈现出真实性与亲切性的特点;而以第三人称展开的叙事文本,其语言又呈现出丰富性与联想性的特点。 相似文献
7.
Effects of extreme floods on macroinvertebrate assemblages in tributaries to the Mohawk River,New York,USA 下载免费PDF全文
Climate change is forecast to bring more frequent and intense precipitation to New York which has motivated research into the effects of floods on stream ecosystems. Macroinvertebrate assemblages were sampled at 13 sites in the Mohawk River basin during August 2011, and again in October 2011, following historic floods caused by remnants of Hurricane Irene and Tropical Storm Lee. The annual exceedance probabilities of floods at regional flow‐monitoring sites ranged from 0.5 to 0.001. Data from the first 2 surveys, and from additional surveys done during July and October 2014, were assessed to characterize the severity of flood impacts, effect of seasonality, and recovery. Indices of total taxa richness; Ephemeroptera, Plecoptera, and Trichoptera (EPT) richness; Hilsenhoff's biotic index; per cent model affinity; and nutrient biotic index‐phosphorus were combined to calculate New York State Biological Assessment Profile scores. Analysis of variance tests were used to determine if the Biological Assessment Profile, its component metrics, relative abundance, and diversity differed significantly (p ≤ .05) among the four surveys. Only total taxa richness and Shannon–Wiener diversity increased significantly, and abundance decreased significantly, following the floods. No metrics differed significantly between the July and August 2014 surveys which indicates that the differences denoted between the August and October 2011 surveys were caused by the floods. Changes in taxa richness, EPT richness, and diversity were significantly correlated with flood annual exceedance probabilities. This study increased our understanding of the resistance and resilience of benthic macroinvertebrate communities by showing that their assemblages were relatively impervious to extreme floods across the region. 相似文献
8.
9.
孙利芹 《河南机电高等专科学校学报》2008,16(3):41-42
推行学分制是当前我国高校教学管理改革一项迫切而重要的措施。文章分析了学分制导向下大学课程的丰富性,进而提出学分制导向下丰富大学课程的几点看法。 相似文献
10.
Many techniques used to evaluate biological community data for effects of wastewater discharge do not discriminate between change and harmful change. A coefficient using the ratio of numbers of taxa lost between an unaffectd reference community and a pollution affected community, to the total number of taxa found in the affected community, provides a better evaluation of detrimental change. The value of the coefficient is determined by both the observed change in community richness as well as change in taxonomic similarity. The coefficient produces values from zero indicating no harmful change to infinity where there is complete loss of a community. Macroinvertebrate data suggests that values exceeding 0.8 are indicative of excessively harmful change in those communities. 相似文献